Flexible Segmented Stents

ABSTRACT

A radially expandable segmented stent, the stent including annular metallic stent segments and connectors interconnecting each segment, the interconnectors are formed from a biodegradable polymer material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 10/171,199,filed Jun. 12, 2002, now allowed, which is a continuation of U.S. patentapplication Ser. No. 09/346,826, filed Jul. 2, 1999, now issued as U.S.Pat. No. 6,409,754.

BACKGROUND OF THE INVENTION

This invention relates to multiple interconnected stents or stentsegments, the interconnections being comprised of lengths of a plasticmaterial. The term “plastic” is used herein to refer to materials whichare capable of being deformed permanently without rupture.

In the prior art, stents are well known for use in opening andreinforcing the interior wall of blood vessels and other body conduits.

Stents are generally tubular, radially expandable and may be of theself-expanding type or may be expandable with an outward pressureapplied to the stent, typically by expansion of an interiorly positionedballoon. Stents are made of various materials such as plastic or metal,metal usually being preferred.

Since stents must be of somewhat rigid design to provide reinforcementsupport and may be required to be of considerable length in order toextend over a lengthy area, it is difficult to resolve this need forrigidity with the need of having a flexible stent which is readilyimplanted by inserting it through a sometimes tortuous curving path asis often encountered in the percutaneous insertion technique typicallyused for implantation of stents. This is further complicated by the factthat stents must be readily expandable upon implantation to provide asupport structure.

It is known that a plurality of stent elements can be looselyinterconnected together by filaments or the like to provide a lengthyflexible stent arrangement. Such arrangements are shown in the followingpatents for example:

U.S. Pat. No. 5,405,377 to Cragg

U.S. Pat. No. 5,665,115 to Cragg

U.S. Pat. No. 5,755,781 to Jayaraman

U.S. Pat. No. 5,443,476 to Schwartz et al.

U.S. Pat. No. 5,135,536 to Hillstead

U.S. Pat. No. 5,035,706 to Gianturco et al.

WO 93/13825 (PCT) to Maeda et al.

The following technical literature is also of interest in this regard:

-   Tracheobronchial Tree: Expandable Metallic Stents Used in    Experimental and Clinical Applications, Work in Progress; Radiology,    February 1986, pp 309-312.-   Experimental intrahepatic Portacaval Anastomosis: Use of Expandable    Gianturco Stents; Radiology, February 1987, 162: 481-485.-   Gianturco Expandable Wire Stents in the Treatment of Superior Vena    Cava Syndrome Recurring After Maximum-Tolerance Radiation; Cancer,    September 1987, Vol. 60, pp 1243-1246.-   Modified Gianturco Expandable Wire Stents in Experimental And    Clinical Use; Cerise, Porto Cervo, May 1987, pp 100-103.

BRIEF SUMMARY OF THE INVENTION

This invention is directed to an improvement in the general concept ofjoined stents or stent segments (hereinafter referred to collectively as“stent segments”) in which a “plastic” material (capable of exhibitingpermanent deformation) extends between stents or stent segments(hereinafter referred to collectively as stent segments) to interconnectthem with a somewhat constrained freedom of motion relative to eachother, i.e., not loosely connected but flexibly connected. The stentsegments are preferably of closed cell design and even more preferablyof the self-expanding type. More precisely, the interconnecting elementsare of a material different than the stent material and are plasticallydeformable.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a schematic showing of a stent according to the invention;

FIG. 2 is a schematic showing of a closed cell stent;

FIG. 3 shows the stent of FIG. 2 expanded in a fragmentary view;

FIG. 4 is a schematic showing of an open cell stent;

FIG. 5 shows the stent of FIG. 4 expanded, and

FIG. 6 is a showing of a preferred connection arrangement for a stent ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a schematic drawing of a flexible segmented stent10 according to the invention is shown. It is preferably comprised of aplurality of closed cell stents or stent segments 12 interconnected byplastic connectors 14.

Stents 12 are most preferably of closed cell construction and of theself-expandable type such as NITINOL stents which are cut or etched fromtubular stock or rolled from cut or etched flat sheet or other shapememory metals which do not themselves exhibit permanent deformation.

Generally speaking, a self-expanding stent tends to return to itsunconstrained or expanded condition. Also, in this type of stent it isgenerally preferred that it be of a closed cell construction. Inaccordance with this invention it has been found to be particularlyadvantageous to use self-expanding elastic material for the stent orstent segment, i.e., a material which is not “plastic” or “deformable”and to use a “plastic” “deformable” material for the connector elements.Such materials as plastic, i.e., polymeric, which may be biodegradable,metals such as gold, or viscoelastic polymers such as polyethylene maybe used. Such connectors provide constrained motion yet some flexibilityof the stent portions relative to each other and allow for permanentexpansion of the combination as needed.

Alternatively, the stents may be of the type which are expandable withan outward radial pressure as is known in the art and may be of closedcell or open cell construction. Such stents may be of metal such asstainless steel, titanium, nickel or any other metal compatible with thebody. However, in this type of combination, the connector elements will,according to the invention, be of a different material than the stentsor stent segments yet the connector elements will be of a “plastic”,i.e., deformable material such as a polymer or the like as pointed outabove.

In use, these stent combinations will allow for the provisions ofrelatively long stents which may be trimmed to any desired length at thetime of the procedure.

FIG. 2 is a specific example of one type of closed cell construction ina stent 14. FIG. 3 shows the closed cells of stent 14 when expanded.

FIG. 4 is an example of open cell construction in a stent 16. FIG. 5shows the open cells of stent 16 when expanded.

In one embodiment of the invention, it relates to self expanding stentsor stent segments interconnected by connector elements of a differentmaterial exhibiting permanent deformation, i.e., “plastic behavior” uponexpansion, the stents preferably being of closed cell construction.

In another embodiment of the invention it relates to balloon expandableor the like stents or stent segments rigidly interconnected bystructural connector elements of a different “plastic” material than thestents or stent segments, preferably polymeric plastic, most preferablybiodegradable, although in the case of a metal stent, the connector maybe of a different metal exhibiting different permanent deformationcharacteristics, i.e., plastic behavior.

Connector elements may be of any of the variety of implantable grademetals or polymeric plastics such as polytetrafluoroethylene,polyethylene, polypropylene, nylon, polyester, polyurethane and othersexhibiting permanent deformation and of a material different from thatof the stent or stent segment per se.

The connector elements may also be of biodegradable material such aspolycaprolactone, polyglycolic acid, polylactic acid and the like, solong as the material exhibits permanent deformation and form astructural part of the stent combination.

If the stents are of metal they may be coated with a biocompatiblematerial such as polyurethane, polyethylene, polytetrafluorethylene,silicone, block copolymers of polyurethane, polyethylene and silicone,biodegradable polymers such as polylactic acid, polyglycolic acid and/orhydroxy butyrate or valerate copolymer.

In such an instance, the connectors may be fused to the coating on eachstent segment to interconnect them.

Most preferably however, interconnection between stents is accomplishedas shown in FIG. 6. In such an arrangement, a raised portion 18 isformed on connector 20 and an opening 22 is formed in stent 24, theopening 22 being shaped to receive portion 18 and interfit therewith. Ofcourse, the reverse arrangement may be used in which the receivedportion 18 is on stent 22 and the opening 22 is on the connector 20.

The connectors are preferably flat and elongated but may be of variousconfigurations such as straight, S-shaped, U-shaped, etc., and ofdifferent cross-section.

The above Examples and disclosure are intended to be illustrative andnot exhaustive. These examples and description will suggest manyvariations and alternatives to one of ordinary skill in this art. Allthese alternatives and variations are intended to be included within thescope of the attached claims. Those familiar with the art may recognizeother equivalents to the specific embodiments described herein whichequivalents are also intended to be encompassed by the claims attachedhereto.

1. A radially expandable stent comprising a plurality of annularmetallic stent segments, said metallic stent segments formed of a shapememory metal, adjacent stent segments being interconnected by aplurality of interconnectors, at least one of which is formed from abiodegradable polymer material.
 2. The radially expandable stent ofclaim 1 wherein the stent segments are of the self-expanding type. 3.The radially expandable stent of claim 1 wherein the stent segments areof the balloon expandable type.
 4. The radially expandable stent ofclaim 1 wherein the stent segments are of closed cell construction. 5.The radially expandable stent of claim 1 wherein the metallic stentsegments are nitinol.
 6. The radially expandable stent of claim 1wherein said biodegradable polymer material comprises at least onemember selected from the group consisting of polycaprolactone,polyglycolic acid, polylactic acid, hydroxy butyrate, hydroxyl valerate,and mixtures thereof.
 7. The radially expandable stent of claim 1wherein the stent segments are coated with a polymeric material and theinterconnecting lengths of plastic material are fused to the polymercoating.
 8. The radially expandable stent of claim 1 wherein thepolymeric coating and the lengths of polymeric material are of thedifferent composition.
 9. The radially expandable stent of claim 8wherein the polymer coating is biodegradable.
 10. The radiallyexpandable stent of claim 1 wherein the stent segments include at leastone anchor point means for receiving a length of polymeric material andthe length of material includes interfitting means for connection to theanchor point means.
 11. The radially expandable stent of claim 10wherein the anchor point means forms a raised portion and theinterfitting means on the length of polymeric material comprises anopening sized to fit over the anchor point means and interlocktherewith.
 12. The radially expandable stent of claim 10 wherein thelength of polymeric material includes at each end a raised portion andthe stent segments each include at least one opening sized to receive araised portion and interlock therewith.
 13. The radially expandablestent of claim 1 wherein each stent segment is designed and arranged asan independent stent body capable of individual support in a bodyvessel.
 14. The radially expandable stent of claim 1 wherein the stentsegments are of closed cell construction and are self-expandable. 15.The radially expandable stent of claim 1 wherein said interconnectorsare flat and elongated.
 16. The radially expandable stent of claim 1wherein the interconnectors are S-shaped, U-shaped or straight.
 17. Theradially expandable stent of claim 1 wherein said biodegradableinterconnectors undergo plastic deformation on expansion of the stent.18. A radially expandable stent, the stent comprising annular stentsegments that are of a material that undergoes permanent deformation onexpansion of the annular stent segments, that annular stent segmentsexhibit different permanent deformation characteristics that the stentsegments, the interconnector elements are biodegradable.
 19. Theradially expandable stent of claim 18 being self expanding.
 20. Aradially expandable stent, the stent comprising stent segments that areof a that are of a balloon expandable construction and are formed from ametal, and the interconnector elements are of a different material, theinterconnector elements exhibiting different permanent deformationcharacteristics than the stent segments, the interconnector elements arebiodegradable.